setTimeout(()=>{
    console.log(1);
    
})

const fs=require('fs')
fs.readFile('./index.js', 'utf-8', (err, data) => {
    console.log(2);
})

setImmediate(()=>{
    console.log(3);
    
})


// 不加延迟则输出顺序不确定，加了则输出123
const start=Date.now()
while(Date.now()-start<50){}

